The present invention relates to scanning devices and systems for generating three dimensional data characterizing the exterior or surface of a scanned object, and more particularly to noncontact scanning devices and systems automated to minimize the need for operator intervention.
The ability to replicate the exterior surface of an article, accurately in three dimensional space, is becoming increasingly useful in a wide variety of fields. Industrial and commercial applications include reverse engineering, inspection of parts and quality control, and for providing digital data suitable for further processing in applications such as computer aided design and automated manufacturing. Educational and cultural applications include the reproduction of three dimensional works of art, museum artifacts and historical objects, facilitating a detailed study of valuable and often fragile objects, without the need to physically handle the object. Medical applications for full and partial scanning of the human body continue to expand, as well as commercial applications providing 3D representations of products in high detail resolution to internet retail catalogs.
In general, three dimensional noncontact scanning involves projecting radiant energy, for example laser light or projected white light structured in patterns, onto the exterior surface of an object, and then using a CCD array, CMOS array, or other suitable sensing device to detect radiant energy reflected by the exterior surface. The energy source and energy detector typically are fixed relative to each other and spaced apart by a known distance to facilitate locating the point of reflection by triangulation. In one approach known as laser line scanning, a planar sheet of laser energy is projected onto the object's exterior surface as a line. The object or the scanner can be moved to sweep the line relative to the surface to project the energy over a defined surface area. In another approach known as white light projection or referred to more broadly as structured light, a light pattern (typically patterned white light stripes) is projected onto the object to define a surface area without requiring relative movement of the object and scanner.
Scanned objects usually are supported on a table or base, which can be moved in a linear or rotary fashion (or both) to expose different regions of the exterior surface to the light source. The light source can be supported movably, or several sources can be used to project the light selectively onto different regions of the exterior surface. Nonetheless, most scanning systems require multiple orientations of the scanned object to provide a complete, uninterrupted scan of the entire exterior surface. At the very least, an object supported on a horizontal table or base must be turned over to provide scanner access to its previously inaccessible “underside.” Frequently, the shape of an object does not lend itself to a simple “turning over” to reveal previously unexposed surface regions, requiring several manual or robotic reorientations of the object between successive scans. The need to reposition the object increases the time, complexity and expense of the scanning process, not only due to the additional scans and repositioning between scans, but also due to the difficulty encountered in registering the separate scans, i.e. properly aligning the scans with respect to each other to position the scans in the same three dimensional space. In conventional scanning systems, the repositioning and reorienting of objects and the merging of the separate scans into a single useful database require considerable skill on the part of the system operator.
In many conventional scanning systems, the table or base supports the scanned object by gravity. The desired number of scanners are disposed above the base, exposing upwardly facing and horizontally facing regions of the exterior surface to energy projected by the scanners while leaving a downwardly facing “underside” of the object unexposed. A published U.S. Patent Application, published under publication no. 2004/0246473 (Hermary et al.), discloses a system in which scanners are positioned beneath an object as well as above the object to expose the underside for scanning. More particularly, a scanning device for logs or boards positions four scanning heads in surrounding relation to a log or board move axially through the system. The scanners, two above the log and two below the log, are spaced in 90 degree increments in a plane perpendicular to the axial direction. The system requires the log or board to be moved axially for scanning, and does not scan the opposite ends of the board or log.
U.S. Pat. No. 7,187,457 (Kobayashi) discloses a system for measuring the size of an object based on two-dimensional projected images. The article to be measured is placed on a transparent glass plate. A frame, movable horizontally with respect to the glass plate, has an upper region that supports a row of photodetectors. A lower portion of the frame supports a row of light emitting diodes. Although the device is capable of measuring the size of the article in the direction in which the photo detectors are arranged, measurements of size in multiple directions would require multiple reorientations of the object.
The forgoing systems, although useful in certain applications, fail to address the feature of generating data sufficient to replicate an entire uninterrupted exterior shape of a scanned three dimensional object, through a single scanning sequence without operator intervention. Certain approaches characterized as “full surface” scans, e.g. the scan of a sculpture standing upright on a pedestal or a medical scan of the head, likewise fail to address this feature, due to a substantial void (bottom of the pedestal, or area of the neck) in the resulting scan data.
In some applications, this void is inconsequential. In other applications, such as the inspection of an industrial part, the replication of a three dimensional work whose entire exterior surface is part of the artistic expression, or the replication of a commercial product in its entirety, the void is critical.
Accordingly, the present invention involves several aspects, each directed to one or more of the following objects:                to provide a noncontact scanning system capable of generating a complete three dimensional scan of an object's entire viewable exterior surface in a single, automated scanning operation;        to provide a noncontact scanning system incorporating a support structure functionally transparent to radiant energy to allow a complete surface scanning while the support structure maintains the object in a viewing volume for scanning;        to provide a process for automatically scanning the exterior surface of an object in a manner that generates redundant data corresponding to overlapping surface regions and employs the redundant data to more effectively merge and align data from multiple scans of the object; and        to provide a totally automated noncontact scanning system usable by unskilled individuals to generate data in a three dimensional coordinate system representing the complete, uninterrupted exterior shape, and if desired further representing the color, of a scanned object.        